1. Field of the Invention
The present invention relates to a so-called thin film magnetic element, in which electric resistance changes according to the relation between the magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer affected by an external magnetic field, and particularly to a thin film magnetic element adaptable for track narrowing.
2. Description of the Related Art
FIG. 18, designated xe2x80x9cPRIOR ART,xe2x80x9d is a sectional view of the structure of a conventional thin film magnetic element as viewed from the air bearing surface (ABS) side.
The thin film magnetic element shown in FIG. 18 is referred to as a xe2x80x9cspin valve thin film magnetic elementxe2x80x9d which is one of GMR (giant magnetoresistive) elements utilizing a giant magnetoresistive effect, for detecting a recording magnetic field from a recording medium such as a hard disk or the like.
The spin valve thin film magnetic element comprises a multilayer film 9 comprising an underlying layer 6, an antiferromagnetic layer 1, a pinned magnetic layer 2, a nonmagnetic conductive layer 3, a free magnetic layer 4, and a protecting layer 7, which are laminated in turn from the bottom. A pair of hard bias layers 5 are formed on both sides of the multilayer film 9, and a pair of electrode layers 8 are formed on the hard bias layers 5. Each of the underlying layer 6 and the protecting layer 7 comprises a Ta (tantalum) film or the like. The track width Tw is determined by the width dimension of the-upper surface of the multilayer film 9.
Generally, the antiferromagnetic layer 1 comprises a Fexe2x80x94Mn (iron-manganese) alloy film or a Nixe2x80x94Mn (nickel-manganese) alloy film, each of the pinned magnetic layer 2 and the free magnetic layer 4 comprises a Nixe2x80x94Fe (nickel-iron) alloy film, the nonmagnetic conductive layer 3 comprises a Cu (copper) film, the hard bias layers 5 comprise a Coxe2x80x94Pt (cobalt-platinum) alloy film, and the electrode layers 8 comprise a Cr (chromium) film.
As shown in FIG. 18, magnetization of the pinned magnetic layer 2 is put into a single magnetic domain state in the Y direction (the direction of a leakage magnetic field from a recording medium; height direction) by an exchange anisotropic magnetic field with the antiferromagnetic layer 1. Magnetization of the free magnetic layer 4 is oriented in the X direction by the influence of a bias magnetic field from the hard bias layers 5.
Namely, the magnetization direction of the pinned magnetic layer 2 is set to be perpendicular to the magnetization direction of the free magnetic layer 4.
In the spin valve thin film magnetic element, a sensing current is supplied to the pinned magnetic layer 2, the nonmagnetic conductive layer 3 and the free magnetic layer 4 from the electrode layers 8 respectively formed on the hard bias layers 5. The movement direction of the recording medium such as a hard disk or the like coincides with the Z direction. When a leakage magnetic field is applied from the recording medium in the Y direction, the magnetization direction of the free magnetic layer 4 is changed from the X direction to the Y direction. As a result, the electric resistance changes based on the relation between the change in the magnetization direction of the free magnetic layer 4 and the pinned magnetization direction of the pinned magnetic layer 2 (this is referred to as the xe2x80x9cmagnetoresistive effectxe2x80x9d), and thus the leakage magnetic field from the recording medium is detected by a voltage change based on the change in the electric resistance value.
However, the conventional thin film magnetic element shown in FIG. 18 has the following problems.
As described above, the magnetization direction of the pinned magnetic layer 2 is put into the single magnetic domain state and pinned in the Y direction, but the hard bias layers 5 magnetized in the X direction are provided on both sides of the pinned magnetic layer 2. Therefore, particularly, magnetization at either end of the pinned magnetic layer 2 is not pinned in the Y direction due to the influence of the bias magnetic fields of the hard bias layers 5.
Namely, the magnetization direction of the free magnetic layer 4 put into the single magnetic domain state in the X direction is not perpendicular to the magnetization direction of the pinned magnetic layer 2 due to magnetization of the hard bias layers 5 in the X direction, particularly, in the vicinities of the side ends of the multilayer film 9. The reason for setting the magnetization directions of the free magnetic layer 4 and the pinned magnetic layer 2 to be perpendicular to each other is that magnetization of the free magnetic layer 4 can be easily changed with a small external magnetic field to greatly change the electric resistance, thereby improving reproduction sensitivity. The other reason is that the perpendicular relation permits the formation of an output waveform having good symmetry.
Furthermore, in the thin film magnetic element shown in FIG. 18, the side surfaces of the multilayer film 9 are inclined, and the inclination angle e of the side surfaces of the multilayer film 9 readily varies with the product. A variation in the inclination angle causes a variation in the length of the free magnetic layer 4 in the track width direction. Namely, the width dimension Ew of the sensitive zone EA exhibiting the magnetoresistive effect also varies to cause the problem of causing a variation in magnetic field sensitivity of the thin film magnetic element.
In the multilayer film 9, the central zone excluding the dead zones DA is a sensitive zone EA which substantially contributes to reproduction of the recording magnetic field and which exhibits the magnetoresistive effect. The width of the sensitive zone EA is shorter than the track width Tw set at the time of formation of the multilayer film 9 by an amount corresponding to the width of the dead zones DA.
In this way, in the magnetoresistive element, the dead zones DA which less contributes to reproduced output are formed in the multilayer film 9 near the both sides thereof, and thus the dead zones DA are only zones in which the DC resistance value (DCR) is increased.
In recent years, the track width Tw of the thin film magnetic element has been further decreased with a further increase in recording density of a magnetic recording medium, and thus the track width Tw has been required to be decreased to 0.5 xcexcm or less. However, the width dimension Dw of the dead zones DA is about 0.1 xcexcm, and with a track width Tw of 0.5 xcexcm or less, the ratio of the width dimension Dw of the dead zones to the track width Tw is increased to cause difficulties in accurately controlling the width dimension Ew of the sensitive zone EA. When the ratio of the width dimension Dw of the dead zones DA to the track width Tw is increased, reproduced output is also decreased.
Furthermore, in the thin film magnetic element shown in FIG. 18, the side surfaces of the multilayer film 9 are inclined, and the inclination angle xcex8 of the side surfaces of the multilayer film 9 readily varies with the product. A variation in the inclination angle causes a variation in the length of the free magnetic layer 4 in the track width direction. Namely, the width dimension Ew of the sensitive zone EA exhibiting the magnetoresistive effect also varies to cause the problem of causing a variation in magnetic field sensitivity of the thin film magnetic element.
FIG. 44, designated as xe2x80x9cPRIOR ART,xe2x80x9d is a sectional view showing the structure of another thin film magnetic element manufactured by a conventional manufacturing method, as viewed from the ABS side.
The thin film magnetic element shown in FIG. 44 is called a spin valve thin film magnetic element which is one of GMR (giant magnetoresistive) elements utilizing the giant magnetoresistive effect, for detecting a recording magnetic field from a recording medium such as a hard disk or the like.
The spin valve thin film magnetic element shown in FIG. 44 comprises a multilayer film 9 comprising a substrate 11, an antiferromagnetic layer 1, a pinned magnetic, layer 2, a nonmagnetic conductive layer 3, and a free magnetic layer 4, which are laminated in turn from the bottom. A pair of longitudinal bias layers 10 are formed on the multilayer film 9, and a pair of electrode layers 8 are formed on the longitudinal bias layers 10.
Generally, each of the antiferromagnetic layer 1 and the longitudinal bias layers 10 comprises a Fe-Mn (iron-manganese) alloy film or a Nixe2x80x94Mn (nickel-manganese) alloy film. Each of the pinned magnetic layer 2 and the free magnetic layer 4 comprises a Nixe2x80x94Fe (nickel-iron) alloy film. The nonmagnetic conductive layer 3 comprises a Cu (copper) film, and the electrode layers 8 comprise a Cr film.
As shown in FIG. 44, magnetization of the pinned magnetic layer 2 is preferably put into the single magnetic domain state in the Y direction (the direction of a leakage magnetic field from a recording medium; height direction) by an exchange anisotropic magnetic field with the antiferromagnetic layer 1. Magnetization of the free magnetic layer 4 is preferably oriented in the X direction by the influence of an exchange anisotropic magnetic field from the longitudinal bias layers 10.
Namely, the magnetization direction of the pinned magnetic layer 2 is set to be perpendicular to the magnetization direction of the free magnetic layer 4.
In the spin valve thin film magnetic element, a sensing current is supplied to the free magnetic layer 4, the nonmagnetic conductive layer 3 and the pinned magnetic layer 2 from the electrode layers 8 respectively formed on the longitudinal bias layers 10. The movement direction of the recording medium such as a hard disk or the like coincides with the Z direction. When a leakage magnetic field is applied from the recording medium in the Y direction, the magnetization direction of the free magnetic layer 4 is changed from the X direction to the Y direction. As a result, the electric resistance changes according to the relation between the change in the magnetization direction of the free magnetic layer 4 and the pinned magnetization direction of the pinned magnetic layer 2 (this is referred to as the xe2x80x9cmagnetoresistive effectxe2x80x9d), and thus the leakage magnetic field from the recording medium is detected by a voltage change based on the change in the electric resistance value.
In manufacturing the spin valve thin film magnetic element shown in FIG. 44, the antiferromagnetic layer 1, the pinned magnetic layer 2, the nonmagnetic conductive layer 3, and the free magnetic layer 4 are continuously successively deposited on the substrate 11 to form the multilayer film 9. Then the longitudinal bias layers 10 and the electrode layers 8 are further continuously deposited on the multilayer film 9.
After the layers from the antiferromagnetic layer 1 to the electrode layers 8 are deposited, first magnetic field annealing must be performed for orienting the magnetization direction of the pinned magnetic layer 2 in the Y direction. Then the second magnetic field annealing must be performed for orienting the magnetization direction of the free magnetic layer 4 in the X direction.
However, in the first magnetic field annealing and the second magnetic field annealing after the layers from the antiferromagnetic layer 1 to the electrode layers 8 are deposited, the exchange anisotropic magnetic field exerting on the interface between the antiferromagnetic layer 1 and the pinned magnetic layer 2. The inclination is changed from the Y direction to the X direction in the second magnetic field annealing. As a result, the magnetization directions of the pinned magnetic layer 2 and the free magnetic layer 4 are not perpendicular to each other to cause the problem of increasing a degree (asymmetry) with which the symmetry of a output signal waveform cannot be obtained.
The above-described problem significantly occurs when the antiferromagnetic layer 1 and the longitudinal bias layers 10 are made of antiferromagnetic materials having the same composition.
The present invention has been achieved for solving the above problems of conventional elements, and an object of the present invention is to provide a thin film magnetic element in which no dead zone is formed in a multilayer film having the magnetoresistive effect so that a track width can be precisely controlled, and a decrease in reproduced output can be prevented.
Another object of the present invention is to provide a method of manufacturing a spin valve thin film magnetic element comprising first and second antiferromagnetic layers which are laminated in the thickness direction with other layers including a pinned magnetic layer and a free magnetic layer provided therebetween, the method comprising annealing the first antiferromagnetic layer in a first magnetic field, and laminating the second antiferromagnetic layer and annealing the second antiferromagnetic layer in a second magnetic field so that the magnetization directions of the pinned magnetic layer and the free magnetic layer can be made perpendicular to each other.
In order to achieve the objects, in accordance with an aspect of the present invention, a thin film magnetic element comprises a multilayer film exhibiting a magnetoresistive effect, and a first antiferromagnetic layer for orienting the magnetization direction of at least one magnetic layer which constitutes the multilayer film, wherein the first antiferromagnetic layer is laminated above or below the multilayer film through a nonmagnetic layer.
With the first antiferromagnetic layer laminated above or below the multilayer film through the nonmagnetic layer, the magnetization direction of a magnetic layer, which is oriented by the first antiferromagnetic layer, is oriented by RKKY (method of measuring exchange force) interaction with the first antiferromagnetic layer. The RKKY interaction exerts only between the antiferromagnetic layer having a thickness with antiferromagnetism and a magnetic layer directly above or below the antiferromagnetic layer, but does not exert on a region deviating from the region directly above or below the antiferromagnetic layer having a thickness with antiferromagnetism.
Therefore, the region of the track width (optical track width) Tw set at the time of formation of the multilayer film substantially contributes to reproduction of a recording magnetic field, and thus functions as the sensitive zone exhibiting the magnetoresistive effect. Namely, the thin film magnetic element of the present invention has an optical track width equal to a magnetic track width, and can thus easily comply with an increase in recording density of a recording medium, as compared with a hard bias system which easily causes difficulties in controlling the magnetic track due to the presence of the dead zones.
Also, no dead zone is formed in the region of the track width (optical track width) Tw set at the time of formation of the multilayer film. Therefore, when the optical track width Tw of the thin film magnetic element is decreased to comply with a higher recording density, a decrease in reproduced output can be suppressed.
Furthermore, in the thin film magnetic element of the present invention, the side surfaces of the multilayer film can be formed perpendicularly to the substrate surface, thereby suppressing a variation in the length of the free magnetic layer in the width direction thereof.
In the present invention, the magnetization direction of the magnetic layer is oriented by RKKY interaction with the first antiferromagnetic layer, and thus exchange coupling force can be strengthened as compared with the case of direct contact between the first antiferromagnetic layer and the magnetic layer.
In the present invention, the nonmagnetic layer is preferably made of a conductive material.
Particularly, the nonmagnetic layer is preferably made of at least one element selected from Ru, Cu, Ag, and Au.
More preferably, the nonmagnetic layer is made of Ru, and has a thickness of 8 to 11 xc3x85 (angstrom).
In the present invention, the nonmagnetic layer is made of a conductive material so that the nonmagnetic layer can be caused to function as a backed layer having a spin filter effect.
When the backed layer having the spin filter effect is provided in contact with the free magnetic layer, the center height of the laminate at which a sensing current flows can be shifted to the backed layer Side as compared with a case without the backed layer. Namely, the center height of the sensing current flow deviates from the free magnetic layer to decrease the strength of a sensing current magnetic field at the position of the free magnetic layer, thereby decreasing the influence of the sensing current magnetic field on variable magnetization of the free magnetic layer. Therefore, asymmetry can be decreased.
The xe2x80x9casymmetryxe2x80x9d means the degree of asymmetry of a reproduced output waveform, and the obtained reproduced output having a symmetry waveform has low asymmetry. Therefore, the reproduced output waveform having asymmetry close to zero has excellent symmetry.
The asymmetry is zero when the magnetization directions of the free magnetic layer and the pinned magnetic layer are perpendicular to each other. When the asymmetry greatly deviates, information from a medium cannot be accurately read to cause an error. Therefore, with lower asymmetry, reproduced signal processing has improved reliability, thereby providing an excellent spin valve thin film magnetic element.
In the present invention, the mean free path of spin-up electrons contributing the magnetoresistive effect can be lengthened to obtain a high rate of change in resistance due to the so-called spin filter effect.
In the spin valve thin film magnetic element, with the sensing current applied, conduction electrons mainly move near a nonmagnetic material having low electric resistance. The conduction electrons include the two types of electrons including spin-up electrons and spin-down electrons which are present in stochastically equal amounts.
In the spin valve thin film magnetic element, the rate of change in magnetoresistance shows positive correlation with the difference between the mean free paths of the two types of conduction electrons.
The spin-down electrons are scattered at the interface between the nonmagnetic material layer and the free magnetic layer regardless of the direction of the applied external magnetic field, and the probability of movement to the free magnetic layer is kept down. Therefore, the mean free path of the spin-down conduction electrons remains shorter than that of the spin-up conduction electrons.
On the other hand, with respect to the spin-up conduction electrons, when the magnetization direction of the free magnetic layer is oriented in parallel with the magnetization direction of the pinned magnetic layer with the external magnetic field applied, the spin-up conduction electrons have the high probability of movement from the nonmagnetic material layer to the free magnetic layer to lengthen the mean free path. However, when the magnetization direction of the nonmagnetic material layer is changed from the parallel state with the magnetization direction of the pinned magnetic layer by the external magnetic field, the probability of scattering at the interface between the nonmagnetic material layer and the free magnetic layer increases to shorten the mean free path of the spin-up conduction electrons.
In this way, the mean free path of the spin-up conduction electrons is greatly changed by the action of the external magnetic field in comparison to the mean free path of the spin-down conduction electrons, thereby significantly changing the difference between the mean free paths. Therefore, the mean free path of all conduction electrons is also greatly changed to increase the rate of change (AR/R) in magnetoresistance of the spin valve thin film magnetic element.
When the backed layer is connected to the free magnetic layer, the spin-up conduction electrons moving in the free magnetic layer move into the backed layer to further lengthen the mean free path of the spin-up conduction electrons in proportional to the thickness of the backed layer. Therefore, the so-called spin filter effect can be exhibited to increase the difference between the mean free paths of the conduction electrons, thereby further increase the rate of change (AR/R) in magnetoresistance of the spin valve thin film magnetic element.
The present invention can be applied to a thin film magnetic element comprising a multilayer film comprising a second antiferromagnetic layer, a pinned magnetic layer in which the magnetization direction is pinned by the second antiferromagnetic layer, a nonmagnetic material layer, and a free magnetic layer in which the magnetization direction changes with an external magnetic field, wherein the first antiferromagnetic layer is laminated above or below the free magnetic layer with the nonmagnetic layer provided therebetween so that the magnetization direction of the free magnetic layer is oriented in a direction crossing the magnetization direction of the pinned magnetic layer by magnetic coupling with the first antiferromagnetic layer.
In the present invention, another antiferromagnetic layer is preferably provided between the nonmagnetic layer and the first antiferromagnetic layer.
The other antiferromagnetic layer has the function to prevent oxidation of the nonmagnetic layer due to contact with the air in deposition of the first antiferromagnetic layer above the nonmagnetic layer in the method of manufacturing a thin film magnetic element of the present invention which will be described below.
As the first antiferromagnetic layer, a pair of antiferromagnetic layers can be formed above or below the nonmagnetic layer to be arranged with a predetermined space therebetween in the track width direction.
The pair of the antiferromagnetic layers orients the magnetization direction of the free magnetic layer in the predetermined direction by RKKY coupling with the free magnetic layer. Namely, the pair of the antiferromagnetic layers functions as side bias layers.
When the first antiferromagnetic layers function as the side bias layers, the thickness of the other antiferromagnetic layer is preferably more than 0 and 30 xc3x85 or less. With the other antiferromagnetic layer having a thickness of 30 xc3x85 or more, it is difficult to make the magnetization direction of the first antiferromagnetic layer intersect the magnetization direction of the second antiferromagnetic layer at right angles in the method of manufacturing a thin film magnetic element of the present invention which will be described below.
Furthermore, a recess having a width dimension corresponding to the track width is preferably formed in the first antiferromagnetic layer.
Particularly, the recess preferably has the side surfaces perpendicular to the surface of the substrate.
In the present invention, the track width of the thin film magnetic element is determined by the width dimension of the recess. Namely, the magnetization direction of a magnetic layer such as the free magnetic layer or the like, in which the magnetization direction changes with the external magnetic field, can be changed only in the region overlapped with the bottom of the recess. The recess can be formed only by cutting the first antiferromagnetic layer having a uniform thickness by reactive ion etching (RIE) or ion milling perpendicularly to the surface of the substrate. Therefore, the recess with an accurate width dimension can be formed. Namely, the track width of the thin film magnetic element can be precisely defined.
In the present invention, the bottom of the recess can be provided in the first antiferromagnetic layer. In this case, the thickness of the region of the first antiferromagnetic layer, which is overlapped with the bottom of the recess, or the total thickness of the region of the first antiferromagnetic layer, which is overlapped with the bottom of the recess, and the other antiferromagnetic layer is preferably 30 xc3x85 or less because the magnetization directions of the first and second antiferromagnetic layers can easily be caused to cross at right angles in the method of manufacturing a thin film magnetic element of the present invention which will be described below.
Alternatively, the bottom of the recess may be provided in the other antiferromagnetic layer.
In this case, the thickness of the region of the other antiferromagnetic layer, which is overlapped with the bottom of the recess, is preferably more than 0 and 30 xc3x85 or less. The total thickness of the region of the first antiferromagnetic layer, which is overlapped with the bottom of the recess, and the other antiferromagnetic layer, or the thickness of the region of the other antiferromagnetic layer, which is overlapped with the bottom of the recess, is a thickness which causes no exchange anisotropic magnetic field between the fist antiferromagnetic layer or the other antiferromagnetic layer and at least one magnetic layer.
Alternatively, the bottom of the recess may be provided in the nonmagnetic layer.
In the present invention, as the other antiferromagnetic layer, a specular reflection layer can be formed by using a material which can form an energy gap having the high probability of specular reflection for maintaining the spin state of conduction electrons, extending the mean free path of conduction electrons by the specular reflection effect.
The other antiferromagnetic layer comprising the specular reflection layer, which extends the mean free path of the conduction electrons by the specular reflection effect, can form a potential barrier at the interface between the antiferromagnetic layer and the nonmagnetic layer, so that the spin-up conduction electrons moving in the free magnetic layer and the nonmagnetic layer can be reflected while maintaining the spin state to further extend the mean free path of the spin-up conduction electrons.
Namely, the mean free path of all conduction electrons can be greatly changed by the action of the external magnetic field to significantly increase the rate of change (xcex94R/R) in magnetoresistance of the spin valve thin film magnetic element.
The other antiferromagnetic layer comprising the specular reflection layer may comprise a single layer film or multilayer film made of, for example, a semi-metal Heusler alloy such as NiMnSb, PtMnSb, or the like. By using such a material, a sufficient potential barrier can be formed between the other antiferromagnetic layer and the adjacent layer, thereby obtaining the sufficient specular reflection effect.
In the present invention, the thickness of the free magnetic layer is preferably set in the range of 15 to 45 xc3x85.
When the free magnetic layer has a relatively small thickness, the difference between the mean free paths of the spin-up conduction electrons and the spin-down conduction electrons is effectively increased by the spin filter effect and the specular reflection effect.
With the free magnetic layer having a thickness of less than 15 xc3x85, the free magnetic layer cannot easily be formed to function as a ferromagnetic material layer, thereby failing to obtain the sufficient magnetoresistive effect.
With the free magnetic layer having a thickness of over 45 xc3x85, the number of the spin-up conduction electrons scattered before reaching the specular reflection layer is increased to undesirably decrease the rate of change in the rate of resistance change with the specular effect.
The pinned magnetic layer preferably comprises a plurality of ferromagnetic material layers having magnetic moments of different magnitudes per unit area, which are laminated through nonmagnetic intermediate layers so that the adjacent ferromagnetic material layers with the nonmagnetic intermediate layer provided therebetween are in a ferrimagnetic state in which the magnetization directions thereof are antiparallel to each other.
When the pinned magnetic layer comprises ferromagnetic material layers laminated with a nonmagnetic intermediate layer provided therebetween in the thickness direction, the magnetization directions of the ferromagnetic material layers are pinned by each other to strongly pin the magnetization direction of the whole pinned magnetic layer in a predetermined direction. Namely, a large value of exchange coupling magnetic field Hex between the second antiferromagnetic layer and the pinned magnetic layer can be obtained. Therefore, in magnetic field annealing for orienting the magnetization direction of the first antiferromagnetic layer in the track width direction after or before magnetic field annealing for orienting the magnetization direction of the second antiferromagnetic layer in the height direction, the longitudinal bias magnetic field applied by the first antiferromagnetic layer can be increased while the magnetization of the pinned magnetic layer is prevented from being inclined in the track width direction and pinned.
Furthermore, a demagnetizing field (dipole magnetic field) due to pinned magnetization of the pinned magnetic layer can be canceled by canceling the static magnetic field coupling between the plurality of ferromagnetic material layers. Therefore, contribution to variable magnetization of the free magnetic layer from the demagnetizing field (bipolar magnetic field) due to pinned magnetization of the pinned magnetic layer can be decreased.
Therefore, the direction of variable magnetization of the tree magnetic layer can be easily corrected in the desired direction, thereby obtaining a thin film magnetic element having excellent symmetry with low asymmetry.
Also, the demagnetizing field (bipolar magnetic field) Hd due to pinned magnetization of the pinned magnetic layer has a nonuniform distribution in which the demagnetizing field is high at the ends, and low at the center in the direction of the element height. Therefore, in some cases, the free magnetic layer is inhibited from being put into the single magnetic domain state. However, by using the above laminated structure for the pinned magnetic layer, the demagnetizing field Hd can be made substantially zero Hd=0, thereby preventing the occurrence of Barkhausen noise due to the nonuniformity in magnetization which is caused by a magnetic domain wall formed in the free magnetic layer.
The free magnetic layer preferably comprises a plurality of ferromagnetic material layers having magnetic moments of different magnitudes of per unit area, which are laminated through nonmagnetic intermediate layers so that the adjacent ferromagnetic material layers with the nonmagnetic intermediate layer provided therebetween are in a ferrimagnetic state in which the magnetization directions thereof are antiparallel to each other. This is because an effect equivalent to the effect of decreasing the thickness of the free magnetic layer can be obtained, and thus magnetization of the free magnetic layer easily changes to improve the magnetic field sensitivity of a magnetoresistive element.
The magnitude of magnetic moment per unit area of each of the ferromagnetic material layers is represented by the product of the saturation magnetization (Ms) and the thickness (t) of the ferromagnetic layer.
Each of the nonmagnetic intermediate layers can be made of an alloy of at least one element of Ru, Rh, Ir, Cr, Re and Cu.
In the present invention, at least one of the plurality of ferromagnetic layers is preferably made of a magnetic material having the following composition.
The composition is represented by the formula CoFeNi in which the composition ratio of Fe is 9 atomic % to 17 atomic % (at %), the composition ratio of Ni is 0.5 atomic % to 10 atomic %, and the balance is the composition ratio of Co.
Also, an intermediate layer made of a CoFe alloy or Co is preferably formed between the nonmagnetic material layer and the ferromagnetic material layer laminated closest to the nonmagnetic material layer. When the intermediate layer is formed, at least one of the plurality of ferromagnetic material layers is preferably made of a magnetic material having the following composition.
The composition is represented by the formula CoFeNi in which the composition ratio of Fe is 7 atomic % to 15 atomic %, the composition ratio of Ni is 5 atomic % to 15 atomic %, and the balance is the composition ratio of Co.
In the present invention, all of the plurality of the ferromagnetic material layers are preferably made of CoFeNi.
In the present invention, in the film structure of nonmagnetic material layer/first free magnetic layer/nonmagnetic intermediate layer/second free magnetic layer, CoFeNi preferably has a Fe composition ratio of 9 atomic % to 17 atomic %, a Ni composition ratio of 0.5 atomic % to 10 atomic %, and a Co composition ratio as the balance. With a Fe composition ratio of over 17 atomic %, magnetostriction is increased to xe2x88x923xc3x9710xe2x88x926 or more in the negative direction, and soft magnetic properties deteriorate.
With a Fe composition ratio of less than 9 atomic %, magnetostriction is increased to 3xc3x9710xe2x88x926 or more, and soft magnetic properties deteriorate.
With a Ni composition ratio of over 10 atomic %, magnetostriction is increased to 3xc3x9710xe2x88x926 or more, and the amount of resistance change (xcex94R/R) and the rate of resistance change (xcex94R/R) are decreased due to Ni diffusion between the nonmagnetic material and the ferromagnetic material layer.
With a Ni composition ratio of less than 0.5 atomic %, magnetostriction is increased to xe2x88x923xc3x9710xe2x88x926 or more in the negative direction.
In the above-described composition range, a coercive force of 790 ampere/meter (A/m) or less can be obtained.
When an intermediate layer made of a CoFe alloy or Co is formed between the nonmagnetic material layer and the ferromagnetic material layer laminated closest to the nonmagnetic material layer, for example, in the film structure of nonmagnetic material layer/intermediate layer (CoFe alloy)/first free magnetic layer/nonmagnetic intermediate layer/second free magnetic layer, CoFeNi preferably has a Fe composition ratio of 7 atomic % to 15 atomic %, a Ni composition ratio of 5 atomic % to 15 atomic %, and a Co composition ratio as the balance. With a Fe composition ratio of over 15 atomic %, magnetostriction is increased to xe2x88x923xc3x9710xe2x88x926 or more in the negative direction, and soft magnetic properties deteriorate.
With a Fe composition ratio of less than 7 atomic %, magnetostriction is increased to 3xc3x97106 or more, and soft magnetic properties deteriorate.
With a Ni composition ratio of over 15 atomic %, magnetostriction is increased to 3xc3x97106 or more.
With a Ni composition ratio of less than 5 atomic %, magnetostriction is increased to xe2x88x923xc3x97106 or more in the negative direction.
In the above-described composition range, a coercive force of 790 (A/m) or less can be obtained. Since the intermediate layer made of CoFe or Co has minus magnetostriction, the Fe composition of the CoFeNi alloy is slightly decreased, and the Ni composition is slightly increased, as compared with a film structure without the intermediate layer between the first free magnetic layer and the nonmagnetic material layer.
Like in the above-described film structure, the intermediate layer made of a CoFe alloy or Co is preferably interposed between the nonmagnetic material layer and the first free magnetic layer because diffusion of a metal element between the first free magnetic layer and the nonmagnetic material layer can be effectively prevented. In the present invention, even when the first antiferromagnetic layer and the second antiferromagnetic layer are made of antiferromagnetic materials having the same composition, the magnetization directions of the first and second antiferromagnetic layers can easily be made intersect at right angles. Therefore, without the external magnetic field applied, the magnetization directions of the free magnetic layer and the pinned magnetic layer can be made to intersect at right angles.
The first antiferromagnetic layer and/or the second antiferromagnetic layer is preferably made of a PtMn alloy. The antiferromagnetic layers may be made of a Xxe2x80x94Mn (wherein X is at least one element of Pd, Ir, Rh, Ru, Os, Ni, and Fe) alloy, or a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 (wherein Xxe2x80x2 is at least one element of Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe, and Kr).
In the PtMn alloy and the alloy represented by the formula Xxe2x80x94Mn, Pt or X is preferably in the range of 37 to 63 at %, and more preferably 47 to 57 at %. The upper and lower limits of the numerical range means xe2x80x9cnot more thanxe2x80x9d and xe2x80x9cnot less thanxe2x80x9d, respectively, unless otherwise specified. In another aspect of the present invention, a thin film magnetic element comprises a first antiferromagnetic layer, a pinned magnetic layer in which the magnetization direction is pinned by the first antiferromagnetic layer, a nonmagnetic material layer, and a free magnetic layer in which the magnetization direction changes with an external magnetic field, wherein a second antiferromagnetic layer is provided above or below the free magnetic layer so that the magnetization direction of the free magnetic layer is oriented in a direction crossing the magnetization direction of the pinned magnetic layer by exchange coupling with the second antiferromagnetic layer, and another antiferromagnetic layer is laminated between the free magnetic layer and the second antiferromagnetic layer.
When the second antiferromagnetic layer is provided above or below the free magnetic layer, the magnetization direction of the free magnetic layer is oriented by an exchange coupling magnetic field with the second antiferromagnetic layer. The exchange coupling magnetic field exerts only between an antiferromagnetic layer having a thickness with antiferromagnetism and a region of a magnetic layer which is located immediately above or below the antiferromagnetic layer, not exerts in the region out of the region immediately below or above the antiferromagnetic layer having a thickness with antiferromagnetism.
Therefore, the region of the track width (optical track width) Tw which is set at the time of formation of the thin film magnetic element, is the sensitive zone which substantially contributes to reproduction of a recording magnetic field and exhibits the magnetoresistive effect. Namely, in the thin film magnetic element of the present invention, the optical track width is substantially the same as the magnetic track width, thereby making it easy to comply with increases in the recording density of a recording medium, in comparison to a hard bias system which is difficult to control the magnetic track width because the dead zones are present.
Since there is no dead zone in the region of the track width (optical track width) which is set at the time of formation of the thin film magnetic element, a decrease in reproduced output can be suppressed when the optical track with Tw of the thin film magnetic element is decreased for complying with a higher recording density.
Furthermore, in the present invention, the side surfaces of the thin film magnetic element can be formed perpendicularly to the surface of the substrate, thereby suppressing a variation in the length of the free magnetic layer in the width direction. The other antiferromagnetic layer has the function to prevent oxidation of the free magnetic layer due to contact with the air in the method of manufacturing a thin film magnetic element of the present invention, which will be described below.
In the present invention, the other antiferromagnetic layer is made of a material which can form an energy gap having the high probability of specular reflection for maintaining the spin state of conduction electrons. Therefore, the other antiferromagnetic layer can be caused to function as a specular reflection layer which extends the mean free path of conduction electrons by the specular reflection effect.
The other antiferromagnetic layer functioning as the specular reflection layer may comprise a single layer film or multilayer film made of, for example, a semi-metal Heusler alloy such as NiMnSb, PtMnSb, or the like.
When the other antiferromagnetic layer functions as the specular reflection layer, the thickness of the free magnetic layer is preferably set in the range of 15 to 45 xc3x85.
The thickness of the other antiferromagnetic layer is preferably more than 0 and 30 xc3x85 or less.
With the other antiferromagnetic layer having a thickness of more than 0 and 30 xc3x85 or less, the magnetization direction of the first antiferromagnetic layer can be easily made to intersect the magnetization direction of the second antiferromagnetic layer at right angles in the method of manufacturing a thin film magnetic element of the present invention which will be described below.
The thickness of the other antiferromagnetic layer is more preferably 10 xc3x85 to 30 xc3x85.
Furthermore, a recess having a width dimension corresponding to the track width is preferably formed in the second antiferromagnetic layer.
Particularly, the recess preferably has the side surfaces perpendicular to the surface of the substrate.
In the present invention, the track width of the thin film magnetic element is determined by the width dimension of the recess. Namely, the magnetization direction of the free magnetic layer can be changed only in the region overlapped with the bottom of the recess. Furthermore, the recess can be formed only by cutting the second antiferromagnetic layer having a uniform thickness by reactive ion etching (RIE) or ion milling perpendicularly to the surface of the substrate. Therefore, the recess with an accurate width dimension can be formed. Namely, the track width of the thin film magnetic element can be precisely defined.
In the present invention, the bottom of the recess may be provided in the second antiferromagnetic layer. In this case, the total thickness of the region of the second antiferromagnetic layer, which is overlapped with the bottom of the recess, and the other antiferromagnetic layer is preferably more than 0 and 30 xc3x85 or less because the magnetization directions of the first and second antiferromagnetic layers can easily be caused to cross at right angles in the method of manufacturing a thin film magnetic element of the present invention which will be described below.
Alternatively the bottom of the recess may be provided in the other antiferromagnetic layer.
In this case, the thickness of the region of the other antiferromagnetic layer, which is overlapped with the bottom of the recess, is preferably more than 0 and 30 xc3x85 or less because the magnetization directions of the first and second antiferromagnetic layers can easily be caused to cross at right angles in use of the method of manufacturing a thin film magnetic element of the present invention which will be described below.
The total thickness of the region of the first antiferromagnetic layer, which is overlapped with the bottom of the recess, and the other antiferromagnetic layer, or the thickness of the region of the other antiferromagnetic layer, which is overlapped with the bottom of the recess, is a thickness which causes no exchange anisotropic magnetic field between the other antiferromagnetic layer and the free magnetic layer.
In the present invention, even when the first antiferromagnetic layer and the second antiferromagnetic layer are made of antiferromagnetic materials having the same composition, the magnetization directions of the first and second antiferromagnetic layers can easily be made to intersect at right angles. Therefore, without the external magnetic field applied, the magnetization directions of the free magnetic layer and the pinned magnetic layer can be made to intersect at right angles.
The pinned magnetic layer preferably comprises a plurality of ferromagnetic material layers having magnetic moments of different magnitudes per unit area, which are laminated through nonmagnetic intermediate layers so that the adjacent ferromagnetic material layers with the nonmagnetic intermediate layer provided therebetween are in a ferrimagnetic state in which the magnetization directions thereof are antiparallel to each other.
When the pinned magnetic layer comprises ferromagnetic material layers laminated with a nonmagnetic intermediate layer provided therebetween in the thickness direction, the magnetization directions of the ferromagnetic material layers are pinned by each other to strongly pin the magnetization direction of the whole pinned magnetic layer in a predetermined direction. Namely, a large value of exchange coupling magnetic field Hex between the first antiferromagnetic layer and the pinned magnetic layer can be obtained. Therefore, in magnetic field annealing for orienting the magnetization direction of the second antiferromagnetic layer in the track width direction after or before magnetic field annealing for orienting the magnetization direction of the first antiferromagnetic layer in the height direction, the longitudinal bias magnetic field applied by the second antiferromagnetic layer can be increased while the magnetization of the pinned magnetic layer is prevented from being inclined in the track width direction and pinned.
Furthermore, a demagnetizing field (dipole magnetic field) due to pinned magnetization of the pinned magnetic layer can be canceled by canceling the static magnetic field coupling between the plurality of pinned material layers. Therefore, contribution to variable magnetization of the free magnetic layer from the demagnetizing field (bipolar magnetic field) due to pinned magnetization of the pinned magnetic layer can be decreased.
Therefore, the direction of variable magnetization of the free magnetic layer can be easily corrected in the desired direction, thereby obtaining a spin valve thin film magnetic element having excellent symmetry with low asymmetry.
The xe2x80x9casymmetryxe2x80x9d means the degree of asymmetry of a reproduced output waveform, and the obtained reproduced output having a symmetry waveform has low asymmetry. Therefore, the reproduced output waveform having asymmetry close to zero has excellent symmetry.
When the magnetization directions of variable magnetization of the free magnetic layer and the pinned magnetization direction of the pinned magnetic layer are perpendicular to each other, the asymmetry is zero. When the asymmetry greatly deviates, information from a medium cannot be accurately read to cause an error. Therefore, with lower asymmetry, reproduced signal processing has improved reliability, thereby providing an excellent spin valve thin film magnetic element. The demagnetizing field Hd (bipolar magnetic field) due to pinned magnetization of the pinned magnetic layer has a nonuniform distribution in which the demagnetizing field is high at the ends, and low at the center in the direction of the element height. Therefore, in some cases, the free magnetic layer is inhibited from being put into the single magnetic domain state. However, by using the above laminated structure for the pinned magnetic layer, the demagnetizing field Hd can be made substantially zero Hd=0, thereby preventing the occurrence of Barkhausen noise due to the nonuniformity in magnetization which is caused by a magnetic domain wall formed in the free magnetic layer.
In a further aspect of the present invention, a thin film magnetic element comprises a first antiferromagnetic layer, a pinned magnetic layer in which the magnetization direction is pinned by the first antiferromagnetic layer, a nonmagnetic material layer, and a free magnetic layer in which the magnetization direction changes with an external magnetic field, wherein a second antiferromagnetic layer is provided above or below the free magnetic layer so that the magnetization direction of the free magnetic layer is oriented in a direction crossing the magnetization direction of the pinned magnetic layer by exchange coupling with the second antiferromagnetic layer, a recess having a width dimension corresponding to the track width is formed in the second antiferromagnetic layer, the first and second antiferromagnetic layers are made of antiferromagnetic materials having the same composition, and the pinned magnetic layer comprises a plurality of ferromagnetic material layers having magnetic moments of different magnitudes per unit area, which are laminated through nonmagnetic intermediate layers so that the adjacent ferromagnetic material layers with the nonmagnetic intermediate layer provided therebetween are in a ferrimagnetic state in which the magnetization directions thereof are antiparallel to each other.
In the present invention, the track width of the thin film magnetic element can be precisely defined. Furthermore, the first and second antiferromagnetic layers can be made of antiferromagnetic materials having the same composition, thereby simplifying the process for manufacturing a thin film magnetic element.
Since the pinned magnetic layer is a ferrimagnetic pinned magnetic layer in a ferrimagnetic state in which the magnetization directions of the adjacent ferromagnetic material layers with the nonmagnetic intermediate layer provided therebetween are antiparallel to each other, the magnetization direction of the pinned magnetic layer can be strongly pinned, for example, with a magnitude of 80 to 160 kA/m. Therefore, the exchange coupling magnetic field of the second antiferromagnetic layer (longitudinal bias layer) for orienting the magnetization direction of the free magnetic layer can be increased, thereby stabilizing the perpendicular state of the magnetization directions of the free magnetic layer and the pinned magnetic layer. Furthermore, a demagnetizing field (dipole magnetic field) due to pinned magnetization of the pinned magnetic layer can be canceled by canceling the static magnetic field coupling between the plurality of ferromagnetic material layers. Therefore, contribution to variable magnetization of the free magnetic layer from the demagnetizing field (bipolar magnetic field) due to pinned magnetization of the pinned magnetic layer can be decreased.
Therefore, the direction of variable magnetization of the free magnetic layer can be easily corrected in the desired direction, thereby obtaining a thin film magnetic element having excellent symmetry with low asymmetry.
Also, the demagnetizing field (bipolar magnetic field) Hd due to pinned magnetization of the pinned magnetic layer has a nonuniform distribution in which the demagnetizing field is high at the ends, and it is low at the center in the direction of the element height. Therefore, in some cases, the free magnetic layer is inhibited from being put into the single magnetic domain state. However, by using the above laminated structure for the pinned magnetic layer, the demagnetizing field Hd can be made substantially zero Hd=0, thereby preventing the occurrence of Barkhausen noise due to the nonuniformity in magnetization which is caused by a magnetic domain wall formed in the free magnetic layer.
In the present invention, the bottom of the recess may be provided in the second antiferromagnetic layer. In this case, the thickness of the region of the second antiferromagnetic layer, which is overlapped with the bottom of the recess, is preferably more than 0 and 30 xc3x85 or less.
The thickness of the region of the second antiferromagnetic layer, which is overlapped with the bottom of the recess, is a thickness which causes no exchange anisotropic magnetic field between the second antiferromagnetic layer and the free magnetic layer.
The free magnetic layer preferably comprises a plurality of ferromagnetic material layers having magnetic moments of different magnitudes per unit area, which are laminated through nonmagnetic intermediate layers so that the adjacent ferromagnetic material layers with the nonmagnetic intermediate layer provided therebetween are in a ferrimagnetic state in which the magnetization directions thereof are antiparallel to each other. This is because an effect equivalent to the effect of decreasing the thickness of the free magnetic layer can be obtained, and thus magnetization of the free magnetic layer easily changes to improve the magnetic field sensitivity of a magnetoresistive element.
The magnitude of magnetic moment per unit area of each of the ferromagnetic material layers is represented by the product of the saturation magnetization (Ms) and the thickness (t) of the ferromagnetic layer.
Each of the nonmagnetic intermediate layers can be made of an alloy of at least one element of Ru, Rh, Ir, Cr, Re and Cu.
In the present invention, at least one of the plurality of ferromagnetic material layers is preferably made of a magnetic material having the following composition.
The composition is represented by the formula CoFeNi in which the composition ratio of Fe is 9 atomic to 17 atomic the composition ratio of Ni is 0.5 atomic % to 10 atomic %, and the balance is the composition ratio of Co.
Also, an intermediate layer made of a CoFe alloy or Co is preferably formed between the nonmagnetic material layer and the ferromagnetic material layer laminated closest to the nonmagnetic material layer. When the intermediate layer is formed, at least one of the plurality of ferromagnetic material layers is preferably made of a magnetic material having the following composition.
The composition is represented by the formula CoFeNi in which the composition ratio of Fe is 7 atomic % to 15 atomic %, the composition ratio of Ni is 5 atomic % to 15 atomic %, and the balance is the composition ratio of Co.
In the present invention, all of the plurality of ferromagnetic material layers are preferably made of CoFeNi.
In the present invention, in the film structure of nonmagnetic material layer/first free magnetic layer/nonmagnetic intermediate layer/second free magnetic layer, CoFeNi preferably has a Fe composition ratio of 9 atomic % to 17 atomic %, a Ni composition ratio of 0.5 atomic % to 10 atomic %, and a Co composition ratio as the balance. With a Fe composition ratio of over 17 atomic %, magnetostriction is increased to xe2x88x923xc3x9710xe2x88x926 or more in the negative direction, and soft magnetic properties deteriorate.
With a Fe composition ratio of less than 9 atomic %, magnetostriction is increased to 3xc3x9710xe2x88x926 or more, and soft magnetic properties deteriorate.
With a Ni composition ratio of over 10 atomic %, magnetostriction is increased to 3xc3x9710xe2x88x926 or more, and the amount of resistance change (xcex94R/R) and the rate of resistance change (xcex94R/R) are decreased due to Ni diffusion between the nonmagnetic material layer and the ferromagnetic material layer.
With a Ni composition ratio of less than 0.5 atomic %, magnetostriction is increased to xe2x88x923xc3x9710xe2x88x926 or more in the negative direction.
In the above-described composition range, a coercive force of 790 (A/m) or less can be obtained.
When an intermediate layer made of a CoFe alloy or Co is formed between the nonmagnetic material layer and the ferromagnetic material layer laminated closest to the nonmagnetic material layer, for example, in the film structure of nonmagnetic material layer/intermediate layer (CoFe alloy)/first free magnetic layer/nonmagnetic intermediate layer/second free magnetic layer, CoFeNi preferably has a Fe composition ratio of 7 atomic % to 15 atomic %, a Ni composition ratio of 5 atomic % to 15 atomic %, and a Co composition ratio as the balance. With a Fe composition ratio of over 15 atomic %, magnetostriction is increased to xe2x88x923xc3x9710xe2x88x926 or more in the negative direction, and soft magnetic properties deteriorate.
With a Fe composition ratio of less than 7 atomic %, magnetostriction is increased to 3xc3x9710xe2x88x926 or more, and soft magnetic properties deteriorate.
With a Ni composition ratio of over 15 atomic, magnetostriction is increased to 3xc3x9710xe2x88x926 or more.
With a Ni composition ratio of less than 5 atomic %, magnetostriction is increased to xe2x88x923xc3x9710xe2x88x926 or more in the negative direction.
In the above-described composition range, a coercive force of 790 (A/m) or less can be obtained. Since the intermediate layer made of CoFe or Co has minus magnetostriction, the Fe composition of the CoFeNi alloy is slightly decreased, and the Ni composition is slightly increased, as compared with a film structure without the intermediate layer between the first free magnetic layer and the nonmagnetic material layer.
Like in the above-described film structure, the intermediate layer made of a CoFe alloy or Co is preferably interposed between the nonmagnetic material layer and the first free magnetic layer because diffusion of a metal element between the first free magnetic layer and the nonmagnetic material layer can be effectively prevented.
The first antiferromagnetic layer and/or the second antiferromagnetic layer is preferably made of a PtMn alloy, a Xxe2x80x94Mn (wherein X is at least one element of Pd, Ir, Rh, Ru, Os, Ni, and Fe) alloy, or a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 (wherein Xxe2x80x2 is at least one element of Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe, and Kr).
In the PtMn alloy or the alloy represented by the formula Xxe2x80x94Mn, Pt or X is preferably in the range of 37 to 63 at %, and more preferably 47 to 57 at %. The upper and lower limits of the numerical range means xe2x80x9cnot more thanxe2x80x9d and xe2x80x9cnot less thanxe2x80x9d, respectively, unless otherwise specified.
In the alloy represented by the formula Ptxe2x80x94Mnxe2x80x94Xxe2x80x2, the total of Xxe2x80x2+Pt is preferably in the range of 37 to 63 at %, and more preferably 47 to 57 at %, and Xxe2x80x2 is preferably in the range of 0.2 to 10 at %. However, when Xxe2x80x2 is at least one element of Pd, Ir, Rh, Ru, Os, Ni, and Fe, Xxe2x80x2 is preferably in the range of 0.2 to 40 at %.
By using an alloy in the above-described appropriate composition range for the first and second antiferromagnetic layers, the first and second antiferromagnetic layers producing a large exchange coupling magnetic field can be obtained by annealing the alloy. Particularly, by using a PtMn alloy, the excellent first and second antiferromagnetic layers can be obtained, in which the exchange coupling magnetic field is 48 kA/m or more, for example, over 64 kA/m, and the blocking temperature at which the exchange coupling magnetic field is lost is as high as 380xc2x0 C.
The above-described alloy has a disordered face centered cubic structure (fcc) in a state immediately after deposition, but it is transformed to a CuAuI-type ordered face-centered tetragonal structure (fct) by heat treatment.
In the present invention, the first antiferromagnetic layer and the second antiferromagnetic layer can be formed by using antiferromagnetic materials having the same composition.
A method of manufacturing a thin film magnetic element of the present invention comprises the steps of (a) depositing a first antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic material layer, and a free magnetic layer to form a multilayer film on a substrate, (b) annealing the multilayer film in a magnetic field of first magnitude at a first heat treatment temperature to pin the magnetization direction of the pinned magnetic layer in a predetermined direction, (c) depositing a second antiferromagnetic layer on the multilayer film, and (d) annealing the multilayer film with the second antiferromagnetic layer laminated thereon in a magnetic field of second magnitude at a second heat treatment temperature to pin the magnetization direction of the free magnetic layer in the direction perpendicular to the magnetization direction of the pinned magnetic layer.
In the present invention, the multilayer film without the second antiferromagnetic layer laminated thereon is annealed in a magnetic field to pin the magnetization direction of the pinned magnetic layer in the predetermined direction, and thus no exchange anisotropic magnetic field occurs in the second antiferromagnetic layer laminated on the multilayer film.
Namely, the exchange anisotropic magnetic field does not occur in the second antiferromagnetic layer until the step (d), thereby facilitating movement of the magnetization direction of the free magnetic layer to the predetermined direction. Therefore, the magnetization direction of the free magnetic layer can easily be pinned perpendicularly to the magnetization direction of the pinned magnetic layer.
The step (a) is preferably performed in a same vacuum deposition apparatus.
In the present invention, in the step (d), the second heat treatment temperature is preferably set to a temperature lower than the blocking temperature at which the exchange coupling magnetic field of the first antiferromagnetic layer is lost.
Furthermore, in the step (d), the second magnitude of the magnetic field is preferably lower than the exchange anisotropic magnetic field of the first antiferromagnetic layer.
The step (a) preferably further comprises the step of laminating another antiferromagnetic layer on the uppermost layer of the multilayer film because oxidation of the uppermost layer of the multilayer film can be prevented.
In the present invention, the other antiferromagnetic layer is made of a material which can form an energy gap having the high probability of specular reflection for maintaining the spin spate of conduction electrons so that the other antiferromagnetic layer can function as a specular reflection layer to extend the mean free path of the conduction electrons by the specular reflection effect.
When the other antiferromagnetic layer functions as the specular reflection layer, the thickness of the free magnetic layer is preferably set in the range of 15 to 45 xc3x85.
With the free magnetic layer having a thickness of less than 15 xc3x85, the free magnetic layer cannot easily be formed to function as a ferromagnetic material layer, thereby failing to obtain the sufficient magnetoresistive effect.
With the free magnetic layer having a thickness of over 45 xc3x85, the number of the spin-up conduction electrons scattered before reaching the specular reflection layer is increased to undesirably decrease the rate of change in the rate of resistance change with the specular effect.
The other antiferromagnetic layer functioning as the specular reflection layer may comprise a single layer film or multilayer film made of, for example, a semi-metal Heusler alloy such as NiMnSb, PtMnSb, or the like.
By using such materials, a sufficient potential barrier can be formed between the other antiferromagnetic layer and the adjacent layer to obtain the sufficient specular effect.
The thickness of the other antiferromagnetic layer is preferably more than 0 and 30 xc3x85 or less.
With the other antiferromagnetic layer having a thickness of more than 0 and 30 xc3x85 or less, no exchange coupling magnetic field occurs in the other antiferromagnetic layer in the step (b), and thus the magnetization direction of the other antiferromagnetic layer can be prevented from being pinned in the same direction as the magnetization direction of the pinned magnetic layer. Therefore, in the step (c), when the second antiferromagnetic layer is laminated on the other antiferromagnetic layer, the magnetization direction of the free magnetic layer can be prevented from being pinned in the same direction as the magnetization direction of the pinned magnetic layer.
The thickness of the other antiferromagnetic layer is more preferably 10 xc3x85 to 30 xc3x85.
In the step (a), a nonmagnetic layer may be laminated in contact with the upper or lower surface of the free magnetic layer, which is away from the nonmagnetic material layer.
In this case, the magnetization direction of the free magnetic layer is oriented by RKKY interaction with the second antiferromagnetic layer through the nonmagnetic layer in the direction intersecting the magnetization direction of the pinned magnetic layer.
When the magnetization direction of the magnetic layer is oriented by RKKY interaction with the second antiferromagnetic layer, exchange coupling force can be strengthened as compared with the case of direct contact between the second antiferromagnetic layer and the magnetic layer.
The nonmagnetic layer is preferably made of a conductive material. The nonmagnetic layer is preferably made of at least one element selected from Ru, Cu, Ag, and Au. Particularly, preferably, the nonmagnetic layer is made of Ru, and has a thickness of 8 to 11 xc3x85.
In the present invention, the nonmagnetic layer is made of a conductive material so that the nonmagnetic layer can be caused to function as a backed layer having a spin filter effect.
When the backed layer having the spin filter effect is provided in contact with the free magnetic layer, the center height of the laminate at which a sensing current flows can be shifted to the backed layer Side as compared with a case without the backed layer. Namely, the center height of the sensing current flow deviates from the free magnetic layer to decrease the strength of a sensing current magnetic field at the position of the free magnetic layer, thereby decreasing the influence of the sensing current magnetic field on variable magnetization of the free magnetic layer. Therefore, asymmetry can be decreased.
The xe2x80x9casymmetryxe2x80x9d means the degree of asymmetry of a reproduced output waveform, and the obtained reproduced output having a symmetry waveform has low asymmetry. Therefore, the reproduced output waveform having asymmetry close to zero has excellent symmetry.
The asymmetry is zero when the magnetization directions of the free magnetic layer and the pinned magnetic layer are perpendicular to each other. When the asymmetry greatly deviates, information from a medium cannot be accurately read to cause an error. Therefore, with lower asymmetry, reproduced signal processing has improved reliability, thereby providing an excellent spin valve thin film magnetic element.
In the present invention, the mean free path of spin-up electrons contributing the magnetoresistive effect can be extended to obtain a high rate of change in resistance due to the so-called spin filter effect.
In the spin valve thin film magnetic element, with the sensing current applied, conduction electrons mainly move near the nonmagnetic material layer having low electric resistance. The conduction electrons include the two types of electrons including spin-up electrons and spin-down electrons which are present in stochastically equal amounts.
In the spin valve thin film magnetic element, the rate of change in magnetoresistance shows positive correlation with the difference between the mean free paths of the two types of conduction electrons.
The spin-down electrons are scattered at the interface between the nonmagnetic material layer and the free magnetic layer regardless of the direction of the applied external magnetic field, and the probability of movement to the free magnetic layer is kept down. Therefore, the mean free path of the spin-down conduction electrons remains shorter than that of the spin-up conduction electrons.
On the other hand, with respect to the spin-up conduction electrons, when the magnetization direction of the free magnetic layer is oriented in parallel with the magnetization direction of the pinned magnetic layer with the external magnetic field applied, the spin-up conduction electrons have the high probability of movement from the nonmagnetic material layer to the free magnetic layer to lengthen the mean free path. However, when the magnetization direction of the free magnetic layer is changed from the parallel state with the magnetization direction of the pinned magnetic layer by the external magnetic field, the probability of scattering at the interface between the nonmagnetic material layer and the free magnetic layer increases to shorten the mean free path of the spin-up conduction electrons.
In this way, the mean free path of the spin-up conduction electrons is greatly changed by the action of the external magnetic field in comparison to the mean free path of the spin-down conduction electrons, thereby significantly changing the difference between the mean free paths. Therefore, the mean free path of all conduction electrons is also greatly changed to increase the rate of change (xcex94R/R) in magnetoresistance of the spin valve thin film magnetic element.
When the backed layer is connected to the free magnetic layer, the spin-up conduction electrons moving in the free magnetic layer can move into the backed layer to further lengthen the mean free path of the spin-up conduction electrons in proportional to the thickness of the backed layer. Therefore, the so-called spin filter effect can be exhibited to increase the difference between the mean free paths of the conduction electrons, thereby further increase the rate of change (xcex94R/R) in magnetoresistance of the spin valve thin film magnetic element.
The manufacturing method of the present invention may comprise the step (a) of laminating in turn the first antiferromagnetic layer, the pinned magnetic layer, the nonmagnetic material layer and the free magnetic layer on the substrate to form the multilayer film, and the step (c) of forming a lift off resist layer having an undercut formed on the lower side thereof on the free magnetic layer, depositing the second antiferromagnetic layer on the multilayer film and then removing the resist layer from the multilayer film.
Alternatively, after the second antiferromagnetic layer is deposited, a pair of resist layers may be laminated on the second antiferromagnetic layer with a space therebetween corresponding to the track width, and then the portion of the second antiferromagnetic layer, which is held between the resist layers, is cut out perpendicularly to the surface of the substrate so that the track width of the thin film magnetic element can precisely be defined.
Alternatively, in the step (c), a pair of resist layers may be deposited with a space therebetween after the second antiferromagnetic layer is formed on the multilayer film, and the portion of the second antiferromagnetic layer, which is held between the resist layers, is cut perpendicularly to the surface of the substrate to form a recess.
In the present invention, the track width of the thin film magnetic element is determined by the width dimension of the recess. Namely, the magnetization direction of the free magnetic layer can be changed only in the region overlapped with the bottom of the recess. Furthermore, the recess can be formed only by cutting the second antiferromagnetic layer having a uniform thickness with reactive ion etching (RIE) or ion milling perpendicularly to the surface of the substrate. Therefore, the recess having an accurate width dimension can be formed. Namely, the track width of the thin film magnetic element can be precisely defined.
In the present invention, the recess may be provided so that the bottom of the recess is located in the second antiferromagnetic layer.
In this case, the thickness of the region of the second antiferromagnetic layer, which is located below the bottom of the recess, or the total thickness of the region of the second antiferromagnetic layer, which is located below the bottom of the recess, and the other antiferromagnetic layer is preferably more than 0 and 30 xc3x85 or less because no exchange coupling magnetic field occurs in the region of the second antiferromagnetic layer, which is located below the bottom of the recess, or the regions of the second antiferromagnetic layer and the other antiferromagnetic layer, which are located below the bottom of the recess.
Alternatively, the recess may be provided so that the bottom of the recess is located in the other antiferromagnetic layer.
In this case, the thickness of the region of the other antiferromagnetic layer, which is located below the bottom of the recess, is preferably more than 0 and 30 xc3x85 or less because no exchange anisotropic magnetic field occurs in the region of the other antiferromagnetic layer, which is located below the bottom of the recess.
Alternatively, the recess may be formed so that the bottom of the recess is located in the nonmagnetic layer.
In the step (a), the pinned magnetic layer is preferably formed by laminating a plurality of ferromagnetic material layers having magnetic moments of different magnitudes per unit area through nonmagnetic intermediate layers.
When the pinned magnetic layer comprises ferromagnetic material layers laminated with a nonmagnetic intermediate layer provided therebetween in the thickness direction, the magnetization directions of the ferromagnetic material layers are pinned by each other to strongly pin the magnetization direction of the whole pinned magnetic layer in a predetermined direction. Namely, a large value of exchange coupling magnetic field Hex, for example, 80 to 160 kA/m, between the first antiferromagnetic layer and the pinned magnetic layer can be obtained. Therefore, in magnetic field annealing for orienting the magnetization direction of the second antiferromagnetic layer in the track width direction after or before magnetic field annealing for orienting the magnetization direction of the first antiferromagnetic layer in the height direction, the longitudinal bias magnetic field applied by the second antiferromagnetic layer can be increased while the magnetization of the pinned magnetic layer is prevented from being inclined in the track width direction and pinned.
Furthermore, a demagnetizing field (dipole magnetic field) due to pinned magnetization of the pinned magnetic layer can be canceled by canceling the static magnetic field coupling between the plurality of ferromagnetic material layers. Therefore, contribution to variable magnetization of the free magnetic layer from the demagnetizing field (bipolar magnetic field) due to pinned magnetization of the pinned magnetic layer can be decreased.
Therefore, the direction of variable magnetization of the free magnetic layer can be easily corrected in the desired direction, thereby obtaining a spin valve thin film magnetic element having excellent symmetry with low asymmetry.
The demagnetizing field (bipolar magnetic field) Hd due to pinned magnetization of the pinned magnetic layer has a nonuniform distribution in which the demagnetizing field is high at the ends, and low at the center in the direction of the element height. Therefore, in some cases, the free magnetic layer is inhibited from being put into the single magnetic domain state. However, by using the above laminated structure for the pinned magnetic layer, the demagnetizing field Hd can be made substantially zero Hd=0, thereby preventing the occurrence of Barkhausen noise due to the nonuniformity in magnetization which is caused by a magnetic domain wall formed in the free magnetic layer.
In the present invention, the pinned magnetic layer may comprise a single ferromagnetic layer.
In the step (a), the free magnetic layer is preferably formed by laminating a plurality of ferromagnetic material layers having magnetic moments of different magnitudes per unit area through nonmagnetic intermediate layers.
In the present invention, the adjacent ferromagnetic layers with the nonmagnetic intermediate layer provided therebetween are in the ferrimagnetic state in which the magnetization directions are antiparallel to each other, and thus an effect equivalent to the effect of decreasing the thickness of the free magnetic layer can be obtained, Therefore, magnetization of the free magnetic layer easily changes to improve the magnetic field sensitivity of a magnetoresistive element.
The magnitude of magnetic moment per unit area of each of the ferromagnetic material layers is represented by the product of the saturation magnetization (Ms) and the thickness (t) of the ferromagnetic layer.
Each of the nonmagnetic intermediate layers can be made of an alloy of at least one element of Ru, Rh, Ir, Cr, Re and Cu.
In the present invention, at least one of the plurality of the ferromagnetic material layers is preferably made of a magnetic material having the following composition.
The composition is represented by the formula CoFeNi in which the composition ratio of Fe is 9 atomic % to 17 atomic %, the composition ratio of Ni is 0.5 atomic % to 10 atomic %, and the balance is the composition ratio of Co.
Also, an intermediate layer made of a CoFe alloy or Co is preferably formed between the nonmagnetic material layer and the ferromagnetic material layer laminated closest to the nonmagnetic material layer. When the intermediate layer is formed, at least one of the plurality of ferromagnetic material layers is preferably made of a magnetic material having the following composition.
The composition is represented by the formula CoFeNi in which the composition ratio of Fe is 7 atomic % to 15 atomic %, the composition ratio of Ni is 5 atomic % to 15 atomic %, and the balance is the composition ratio of Co.
In the present invention, all of the plurality of the ferromagnetic material layers are preferably made of CoFeNi.
In the present invention, in the film structure of nonmagnetic material layer/first free magnetic layer/nonmagnetic intermediate layer/second free magnetic layer, CoFeNi preferably has a Fe composition ratio of 9 atomic % to 17 atomic %, a Ni composition ratio of 0.5 atomic % to 10 atomic %, and a Co composition ratio as the balance. With a Fe composition ratio of over 17 atomic %, magnetostriction is increased to xe2x88x923xc3x9710xe2x88x926 or more in the negative direction, and soft magnetic properties deteriorate.
With a Fe composition ratio of less than 9 atomic %, magnetostriction is increased to 3xc3x9710xe2x88x926 or more, and soft magnetic properties deteriorate.
With a Ni composition ratio of over 10 atomic %, magnetostriction is increased to 3xc3x9710xe2x88x926 or more, and the amount of resistance change (xcex94R/R) and the rate of resistance change (xcex94R/R) are decreased due to Ni diffusion between the nonmagnetic material layer and the ferromagnetic material layer.
With a Ni composition ratio of less than 0.5 atomic %, magnetostriction is increased to xe2x88x923xc3x9710xe2x88x926 or more in the negative direction.
In the above-described composition range, a coercive force of 790 (A/m) or less can be obtained.
When the intermediate layer made of a CoFe alloy or Co is formed between the nonmagnetic material layer and the ferromagnetic material layer laminated closest to the nonmagnetic material layer, for example, in the film structure of nonmagnetic material layer/intermediate layer (CoFe alloy)/first free magnetic layer/nonmagnetic intermediate layer/second free magnetic layer, CoFeNi preferably has a Fe composition ratio of 7 atomic % to 15 atomic %, a Ni composition ratio of 5 atomic % to 15 atomic %, and a Co composition ratio as the balance. With a Fe composition ratio of over 15 atomic %, magnetostriction is increased to xe2x88x923xc3x9710xe2x88x926 or more in the negative direction, and soft magnetic properties deteriorate.
With a Fe composition ratio of less than 7 atomic %, magnetostriction is increased to 3xc3x9710xe2x88x926 or more, and soft magnetic properties deteriorate.
With a Ni composition ratio of over 15 atomic %, magnetostriction is increased to 3xc3x9710xe2x88x926 or more.
With a Ni composition ratio of less than 5 atomic %, magnetostriction is increased to xe2x88x923xc3x9710xe2x88x926 or more in the negative direction.
In the above-described composition range, a coercive force of 790 (A/m) or less can be obtained. Since the intermediate layer made of CoFe or Co has minus magnetostriction, the Fe composition of the CoFeNi alloy is slightly decreased, and the Ni composition is slightly increased, as compared with a film structure without the intermediate layer between the first free magnetic layer and the nonmagnetic material layer.
Like in the above-described film structure, the intermediate layer made of a CoFe alloy or Co is preferably interposed between the nonmagnetic material layer and the first free magnetic layer because diffusion of a metal element between the first free magnetic layer and the nonmagnetic material layer can be effectively prevented.
In the present invention, even when the first and second antiferromagnetic layers are formed by using antiferromagnetic materials having the same composition, the magnetization direction of the free magnetic layer can easily be pinned in the direction perpendicular to the magnetization direction of the pinned magnetic layer.
The first antiferromagnetic layer and/or the second antiferromagnetic layer is preferably made of a PtMn alloy, a Xxe2x80x94Mn (wherein X is at least one element of Pd, Ir, Rh, Ru, Os, Ni, and Fe) alloy, or a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 (wherein Xxe2x80x2 is at least one element of Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe, and Kr).
In the PtMn alloy or the alloy represented by the formula Xxe2x80x94Mn, Pt or X is preferably in the range of 37 to 63 at %, and more preferably 47 to 57 at %. The upper and lower limits of the numerical range means xe2x80x9cnot more thanxe2x80x9d and xe2x80x9cnot less thanxe2x80x9d, respectively, unless otherwise specified.
In the alloy represented by the formula Ptxe2x80x94Mnxe2x80x94Xxe2x80x2, the total of Xxe2x80x2+Pt is preferably in the range of 37 to 63 at %, and more preferably 47 to 57 at %, and Xxe2x80x2 is preferably in the range of 0.2 to 10 at %. However, when Xxe2x80x2 is at least one element of Pd, Ir, Rh, Ru, Os, Ni, and Fe, Xxe2x80x2 is preferably in the range of 0.2 to 40 at %. By using an alloy in the above-described appropriate composition range for the first and second antiferromagnetic layers, the first and second antiferromagnetic layers producing a large exchange coupling magnetic field can be obtained by annealing the alloy. Particularly, by using a PtMn alloy, the excellent first and second antiferromagnetic layers can be obtained, in which the exchange coupling magnetic field is 48 kA/m or more, for example, over 64 kA/m, and the blocking temperature at which the exchange coupling magnetic field is lost is as high as 380xc2x0 C.
The above-described alloy has a disordered face-centered cubic structure (fcc) in a state immediately after deposition, but it is transformed to a CuAuI-type ordered face-centered tetragonal structure (fct) by heat treatment.
In the present invention, the first antiferromagnetic layer and the longitudinal bias layer can be formed by using antiferromagnetic materials having the same composition.